Sheet-metal bending

Set the material, thickness, and inside bend radius once at the top; every tab uses them. Leave the K-factor empty to take it from the table (or measure your own on the last tab). Millimetres and inches are switchable; values convert.

Bend allowance — BA = π/180 × A × (R + K·T), outside setback OSSB = tan(A/2) × (R + T), and bend deduction BD = 2 × OSSB − BA. A is the angle the sheet is bent through (90° for a right angle).
Flat pattern — list flange lengths with the bend after each (angle and up/down). With outside dimensions, each flat segment is the flange minus its setbacks; the blank is the segments plus a BA per bend. The table gives where each bend region starts, its centre line, and where it ends, measured from the left edge of the blank, and the profile and blank are drawn.
Press brake — air-bending force F = 1.42 × Rm × T² × L / V (Rm tensile strength in MPa). The suggested V-die is about 8 × T up to 3 mm, 10 × T to 10 mm, then 12 × T; the inside radius comes out near V/6.4 and the shortest flange near 0.7 × V.
K-factor & radius guide — back-calculate K from a measured test strip, and see typical minimum inside radii and K-factors (by R/T) for common sheet materials.

Data sources: standard bend allowance and deduction formulas; K-factors are typical air-bending values; tonnage formula and V-die rules are the common press-brake manufacturer rules of thumb.

Starting points — verify with your press-brake and tooling manufacturer, and bend a test piece before cutting a batch. Grain direction, temper, and tooling wear all shift K and springback.

Share link copies a URL that opens this tool exactly as you have it set up. It carries the material, thickness, bend radius and flange list. Opening a link replaces your own saved settings for the tool; a Restore my settings button brings them back. To write a link by hand, use units, mat, t, r — for example /tools/sheet-metal/?units=mm&mat=mild&t=2&r=2.

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